Non-combustible polymer electrolyte, preparation method thereof and secondary battery

Abstract

The invention discloses a non-combustible polymer electrolyte, a preparation method thereof and a secondary battery, and belongs to the technical field of lithium batteries. The preparation raw materials of the non-combustible polymer electrolyte at least comprise a lithium-conducting monomer, a flame-retardant monomer and a solvent, and meanwhile, the mass of the lithium-conducting monomer and the solvent and the proportion of the lithium-conducting monomer and the solvent in the total mass of the lithium-conducting monomer, the solvent and the flame-retardant monomer are limited. The polymer electrolyte is prepared through synergism of the lithium-conducting monomer, the flame-retardant monomer, the solvent and the like, and the prepared polymer electrolyte not only has incombustibility, but also has excellent electrochemical performance. When the composite material is applied to a lithium battery, excellent electrochemical performance can be maintained while non-combustibility is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular to a non-flammable polymer electrolyte and a preparation method thereof, and a secondary battery. Background Art

[0002] Lithium batteries play a vital role in people's lives, driven by demand for electric vehicles and energy storage devices. However, the liquid electrolytes used in lithium batteries have inherent safety risks.

[0003] In response to the problems of liquid electrolytes, solid electrolytes are considered to be potential candidates for future development. Solid electrolytes can be roughly divided into inorganic solid electrolytes and polymer solid electrolytes. Although inorganic solid electrolytes generally exhibit excellent thermal stability and high ionic conductivity, their interfacial compatibility with electrodes is poor, resulting in rigid "point-to-point" contact and inefficient ion / electron transfer. Polymer solid electrolytes have the advantages of simple processing and high flexibility, resulting in low interfacial resistance between electrodes and electrolytes. Polyethylene oxide (PEO) is one of the most commonly used systems for polymer electrolytes, but the limited chain motion of PEO at room temperature leads to poor ionic conductivity, limiting its commercial application. In addition, PEO is a flammable polymer with low thermal stability, which poses a safety hazard to the battery. Therefore, it is urgent to develop a polymer electrolyte that takes into account both electrochemical performance and safety performance to meet the standards of high-performance lithium batteries. Summary of the invention

[0004] Based on this, the present invention provides a non-flammable polymer electrolyte and a preparation method thereof, and a secondary battery to solve the above technical problems.

[0005] In a first aspect of the present invention, a non-flammable polymer electrolyte is provided, wherein the raw materials for preparing the non-flammable polymer electrolyte at least include a lithium-conducting monomer, a flame-retardant monomer, and a solvent;

[0006] The lithium-conducting monomer comprises a monomer having an acryloyl group and a morpholine group; the flame-retardant monomer comprises a vinyl phosphorus-containing monomer; the solvent comprises an ionic liquid; wherein,

[0007]

[0008] In some embodiments, the mass ratio of the lithium-conducting monomer to the solvent is 1.2 to 2.9:1.

[0009] In some embodiments, the lithium-conducting monomer comprises at least one of the following structural formulas:

[0010]

[0011] Preferably, in the raw materials for preparing the non-combustible polymer electrolyte, the mass fraction of the lithium-conducting monomer is 20% to 40%.

[0012] In some embodiments, the flame-retardant monomer includes at least one of dimethyl vinyl phosphate, diethyl vinyl phosphate, dipropyl vinyl phosphate, and diisopropyl vinyl phosphate;

[0013] Preferably, in the raw materials for preparing the non-combustible polymer electrolyte, the mass fraction of the flame-retardant monomer is 20% to 40%.

[0014] In some embodiments, in the raw materials for preparing the non-combustible polymer electrolyte, the mass fraction of the solvent is 10% to 18%;

[0015] Preferably, the ionic liquid includes a fluorosulfonamide-based anion;

[0016] Preferably, the ionic liquid satisfies at least one of items (1) to (2):

[0017] (1) At 25°C and 1 atm, the conductivity ≥ 0.1 S / m;

[0018] (2) At 25°C and 1 atm, the viscosity ≤ 0.1 Pa·s;

[0019] Preferably, the ionic liquid includes at least one of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-butyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide, and N-methyl-N-butylpyrrolidinium bis(trifluoromethylsulfonyl)imide.

[0020] In some embodiments, the raw materials for preparing the non-combustible polymer electrolyte further include a crosslinking monomer, a lithium salt, and an initiator.

[0021] In some embodiments, the crosslinking monomer includes a monomer containing more than 2 vinyl groups;

[0022] Preferably, the crosslinking monomer includes at least one of triallyl phosphate and triallyl phosphite;

[0023] Preferably, in the raw materials for preparing the non-combustible polymer electrolyte, the mass fraction of the crosslinking monomer is 2% to 8%.

[0024] In some embodiments, the lithium salt includes a fluorosulfonamide-type lithium salt;

[0025] Preferably, the lithium salt includes at least one of lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium hexafluorophosphate;

[0026] Preferably, in the raw materials for preparing the non-flammable polymer electrolyte, the mass fraction of the lithium salt is 10% to 30%.

[0027] In some embodiments, the initiator includes at least one of benzoyl peroxide, potassium persulfate, ammonium persulfate, azobisisobutyronitrile, and azobisisoheptonitrile;

[0028] Preferably, in the raw materials for preparing the non-flammable polymer electrolyte, the mass fraction of the initiator is 0.5% to 1.5%.

[0029] In a second aspect of the present invention, there is provided a method for preparing the non-flammable polymer electrolyte described in the first aspect above, and the preparation method includes the following steps:

[0030] Mix the lithium-ion conductive monomer, the flame retardant monomer, the cross-linking monomer, and the solvent uniformly, add the initiator and the lithium salt, and mix to obtain an electrolyte precursor solution;

[0031] Heat and cure to obtain a non-flammable polymer electrolyte;

[0032] Preferably, the temperature for heat curing is 40°C to 70°C, and the time is 12 h to 48 h;

[0033] More preferably, the temperature for heat curing is 60°C, and the time is 24 h.

[0034] In a third aspect of the present invention, there is provided a secondary battery, including a positive electrode, a negative electrode, and a non-flammable polymer electrolyte;

[0035] The non-flammable polymer electrolyte is the non-flammable polymer electrolyte described in the first aspect above, or the non-flammable polymer electrolyte prepared by the preparation method described in the second aspect above;

[0036] Preferably, the secondary battery is a lithium battery;

[0037] More preferably, the electrolyte precursor is injected into the positive electrode sheet, the separator, and the negative electrode sheet stacked in sequence, and heat cured in situ to form a non-flammable polymer electrolyte.

[0038] The beneficial technical effects of the present invention are as follows:

[0039] The present invention prepares a polymer electrolyte through the synergistic action of a lithium-conducting monomer, a flame-retardant monomer, a solvent, etc. Among them, the lithium-conducting monomer containing acryloyl and morpholine groups used has a relatively low surface electrostatic potential, can form abundant lithium bonds with lithium ions, effectively promotes the dissociation of lithium salts and provides sites for lithium-ion transport. At the same time, the interaction between lithium ions and the lithium-conducting monomer is regulated through the hydrogen bond between an ionic liquid solvent and the lithium-conducting monomer containing acryloyl and morpholine groups to promote the transport of lithium ions, so that the polymer electrolyte has a high ionic conductivity. Furthermore, the flame-retardant monomer used can release PO· at high temperatures, capture free radicals (such as HO·, H·) in the combustion chain reaction, and interrupt the combustion reaction. The highly cross-linked structure can also improve the condensed-phase carbonization performance of the polymer matrix and reduce the generation of combustible gaseous products. The polymer electrolyte prepared by the present invention not only has non-flammability but also excellent electrochemical properties. Detailed Description of the Invention

[0040] Reference will now be made in detail to embodiments of the invention, one or more examples of which are described below. Each example is provided by way of explanation, not limitation of the invention. Indeed, it will be apparent to those skilled in the art that various modifications and variations can be made to the invention without departing from the scope or spirit of the invention. For example, features illustrated or described as part of one embodiment can be used in another embodiment to yield a still further embodiment.

[0041] Accordingly, it is intended that the invention cover such modifications and variations that fall within the scope of the appended claims and their equivalents. Other objects, features, and aspects of the invention are disclosed in or are apparent from the following detailed description. Those of ordinary skill in the art will understand that this discussion is only a description of exemplary embodiments and is not intended to limit the broader aspects of the invention.

[0042] In the present invention, among the technical features described in an open-ended manner, a closed technical solution composed of the listed features is included, as well as an open technical solution containing the listed features.

[0043] In the present invention, regarding numerical ranges, unless otherwise specified, the above numerical ranges are considered continuous and include the minimum and maximum values of the range, as well as each value between such minimum and maximum values. Further, when the range refers to integers, each integer between the minimum and maximum values of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed in the present invention should be understood to include any and all sub-ranges subsumed therein.

[0044] In the present invention, regarding the unit of the data range, if the unit is only attached after the right endpoint, it means that the units of the left endpoint and the right endpoint are the same. For example, 100~150nm means that the units of both the left endpoint "100" and the right endpoint "150" are nm (nanometers).

[0045] If there is no special instruction, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0046] If there is no special instruction, all technical features and optional technical features of the present invention can be combined with each other to form new technical solutions.

[0047] If there is no special instruction, all steps of the present invention can be carried out in sequence or randomly, and preferably in sequence. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) carried out in sequence, or may also include steps (b) and (a) carried out in sequence. For example, when it is mentioned that the method may further include step (c), it means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may also include steps (a), (c) and (b), or may also include steps (c), (a) and (b), etc.

[0048] If there is no special instruction, the "including" and "comprising" mentioned in the present application mean open-ended, and can also be closed-ended. For example, the "including" and "comprising" can mean that other components not listed can also be included or comprised, or can also mean that only the components listed are included or comprised.

[0049] Aiming at the problem in the traditional technology that it is impossible to balance the electrochemical performance and the safety performance, the present invention provides a non-flammable polymer electrolyte, its preparation method and application, so as to solve the above-mentioned technical problems existing in the traditional polymer electrolyte.

[0050] In the first aspect of the present invention, a non-flammable polymer electrolyte is provided. The raw materials for preparing the non-flammable polymer electrolyte at least include a lithium-conducting monomer, a flame-retardant monomer, and a solvent;

[0051] The lithium-conducting monomer includes a monomer having an acryloyl group and a morpholine group; the flame-retardant monomer includes a vinyl phosphorus-containing monomer; the solvent includes an ionic liquid; wherein, the dosages of the lithium-conducting monomer, the flame-retardant monomer and the solvent satisfy:

[0052]

[0053] The present invention prepares a polymer electrolyte by synergistically using a lithium-conducting monomer, a flame-retardant monomer, a solvent, etc. Among them, the lithium-conducting monomer used has a low surface electrostatic potential and can form abundant lithium bonds with lithium ions, effectively promoting the dissociation of lithium salts and providing sites for lithium-ion transport. At the same time, the interaction between lithium ions and the lithium-conducting monomer is regulated through the hydrogen bond between the solvent and the lithium-conducting monomer to promote the transport of lithium ions, so that the polymer electrolyte has a high ionic conductivity. Furthermore, the flame-retardant monomer used can release PO· at high temperatures, capture free radicals (such as HO·, H·) in the combustion chain reaction, and interrupt the combustion reaction. The highly cross-linked structure can also improve the condensed-phase carbonization performance of the polymer matrix and reduce the generation of combustible gaseous products. The polymer electrolyte of the present invention not only has non-flammability but also excellent electrochemical properties.

[0054] It can be understood that if the total mass of the lithium-conducting monomer and the solvent used in the present invention accounts for less than 42% of the total mass of the lithium-conducting monomer, the solvent and the flame-retardant monomer, the proportion of the lithium-conducting monomer and the solvent in the polymer matrix is too low, and the corresponding lithium-ion complex conduction sites are too few, resulting in a decrease in ionic conductivity. However, if it is higher than 75%, the proportion of the phosphorus-containing flame-retardant monomer in the polymer matrix is too low, and the corresponding amount of PO· that can be released is too small, resulting in a significant reduction in the flame retardancy of the electrolyte.

[0055] In some embodiments, the mass ratio of the lithium-conducting monomer to the solvent is 1.2-2.9:1, including but not limited to 1.2:1, 1.5:1, 1.8:1, 2:1, 2.2:1, 2.4:1, 2.6:1, 2.9:1.

[0056] It can be understood that too large or too small mass ratio of the lithium-conducting monomer to the solvent in the present invention will also significantly affect the ionic conductivity of the polymer electrolyte. If the mass ratio of the lithium-conducting monomer to the solvent is too low, the interaction between the lithium-conducting monomer and the solvent will be significantly weakened, resulting in an enhanced coordination effect between the lithium-conducting monomer and lithium ions, which is not conducive to the diffusion and conduction of lithium ions. On the contrary, if the mass ratio of the lithium-conducting monomer to the solvent is too high, the interaction between the solvent and the lithium-conducting monomer will be significantly enhanced, resulting in a weakened coordination effect between the lithium-conducting monomer and lithium ions, which is also not conducive to the dissociation and conduction of lithium salts.

[0057] In some embodiments, the lithium-conducting monomer includes at least one of the following structural formulas:

[0058]

[0059] In the present invention, the compound corresponding to structural formula (1) is denoted as Compound 1, with a CAS number of: 5117-12-4; the compound corresponding to structural formula (2) is denoted as Compound 2, with a CAS number of: 5117-13-5; the compound corresponding to structural formula (3) is denoted as Compound 3 with a CAS number of: 51944-66-2; the compound corresponding to structural formula (4) is denoted as Compound 4 with a CAS number of: 52736-33-1; the compound corresponding to structural formula (5) is denoted as Compound 5 with a CAS number of: 97842-81-4; the compound corresponding to structural formula (6) is denoted as Compound 6 with a CAS number of: 97842-77-8.

[0060] It can be understood that the acryloylmorpholine compound used in the present invention has a relatively low surface electrostatic potential, can form abundant lithium bonds with lithium ions, effectively promotes the dissociation of lithium salts and provides sites for lithium ion transport.

[0061] In some embodiments, in the raw materials for preparing the non-flammable polymer electrolyte, the mass ratio of the lithium-conducting monomer is 20% to 40%; including but not limited to 20%, 25%, 30%, 35%, 40%.

[0062] In some embodiments, the flame retardant monomer includes at least one of dimethyl vinyl phosphate, diethyl vinyl phosphate, dipropyl vinyl phosphate, and diisopropyl vinyl phosphate.

[0063] In some embodiments, in the raw materials for preparing the non-flammable polymer electrolyte, the mass ratio of the flame retardant monomer is 20% to 40%; including but not limited to 20%, 25%, 30%, 35%, 40%.

[0064] In some embodiments, in the raw materials for preparing the non-flammable polymer electrolyte, the mass fraction of the solvent is 10% to 18%; including but not limited to 10%, 12%, 14%, 16%, 18%.

[0065] In some embodiments, the ionic liquid includes a fluorosulfonamide-based anion.

[0066] In some embodiments, the ionic liquid satisfies at least one of items (1) to (2):

[0067] (1) At 25°C and 1 atm, the conductivity ≥ 0.1 S / m;

[0068] (2) At 25°C and 1 atm, the viscosity ≤ 0.1 Pa·s;

[0069] Preferably, the ionic liquid includes a fluorosulfonamide-based anion and satisfies at least one of the above (1) to (2).

[0070] In some embodiments, the ionic liquid includes at least one of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-butyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide, and N-methyl-N-butylpyrrolidinium bis(trifluoromethanesulfonyl)imide.

[0071] It can be understood that the present invention uses a non-flammable ionic liquid instead of a flammable carbonate solvent as a solvent, which can further reduce the flammability of the polymer electrolyte. At the same time, the ionic liquid of the present invention has high ionic conductivity and low viscosity, which can promote the transport of lithium ions. At the same time, the interaction between lithium ions and acryloylmorpholine compounds can be regulated through the hydrogen bond interaction between it and acryloylmorpholine compounds to promote the transport of lithium ions, thereby further improving the ionic conductivity of the polymer electrolyte.

[0072] In some embodiments, the raw materials for preparing the non-flammable polymer electrolyte further include a crosslinking monomer, a lithium salt, and an initiator.

[0073] In some embodiments, the crosslinking monomer includes a monomer containing more than 2 vinyl groups.

[0074] In some embodiments, the crosslinking monomer includes at least one of triallyl phosphate and triallyl phosphite.

[0075] It can be understood that both the flame retardant monomer and the crosslinking monomer used in the present invention contain vinyl groups and phosphorus groups. Among them, the phosphorus-containing group can release PO· at high temperatures, capture free radicals (such as HO·, H·) in the combustion chain reaction, and interrupt the combustion reaction. The highly crosslinked structure can improve the condensed-phase carbonization performance of the polymer matrix and reduce the generation of flammable gaseous products. Both the flame retardant monomer and the crosslinking monomer contain vinyl groups, which can participate in the polymerization reaction, thereby fixing the phosphorus-containing flame retardant group to the polymer backbone and enhancing the carbonization flame retardant effect.

[0076] In some embodiments, in the raw materials for preparing the non-flammable polymer electrolyte, the mass fraction of the crosslinking monomer is 2% to 8%; including but not limited to 2%, 4%, 6%, 8%.

[0077] In some embodiments, the lithium salt includes a fluorosulfonamide-type lithium salt.

[0078] In some embodiments, the lithium salt includes at least one of lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium hexafluorophosphate.

[0079] In some embodiments, in the raw materials for preparing the non-flammable polymer electrolyte, the mass fraction of the lithium salt is 10% to 30%; including but not limited to 10%, 15%, 20%, 25%, 30%.

[0080] In some embodiments, the initiator includes at least one of benzoyl peroxide, potassium persulfate, ammonium persulfate, azobisisobutyronitrile, and azodiisovaleronitrile.

[0081] In the raw materials for preparing the non-flammable polymer electrolyte, in some embodiments, the mass fraction of the initiator is 0.5% to 1.5%; including but not limited to 0.5%, 0.8%, 1.0%, 1.4%, 1.5%.

[0082] In a second aspect of the present invention, there is provided a method for preparing the non-flammable polymer electrolyte described in the first aspect above. The preparation method includes the following steps:

[0083] Mix the lithium-ion conducting monomer, the flame retardant monomer, the cross-linking monomer, and the solvent uniformly, add the initiator and the lithium salt, and mix to obtain an electrolyte precursor solution; heat and cure to obtain a non-flammable polymer electrolyte.

[0084] In some embodiments, the preparation method includes: mixing the lithium-ion conducting monomer, the flame retardant monomer, the cross-linking monomer, and the solvent uniformly by mass percentage, adding the initiator and the lithium salt, and mixing to obtain an electrolyte precursor solution; heat and cure to obtain a non-flammable polymer electrolyte.

[0085] It can be understood that the mass percentage is based on the mass percentage of the above raw materials for the polymer electrolyte. Exemplarily, it can be: lithium-ion conducting monomer 20% to 40%; flame retardant monomer 20% to 40%; solvent 10% to 18%; cross-linking monomer 2% to 8%; lithium salt 10 to 30%; initiator 0.5% to 1.5%; and, Determine the amounts of each raw material. It is further preferable that the mass ratio of the lithium-ion conducting monomer to the solvent is 1.2 to 2.9:1.

[0086] It can be understood that before heating and curing in the present invention, the electrolyte precursor solution can be injected into the battery cell, encapsulated, and infiltrated.

[0087] In some embodiments, the temperature for heating and curing is 40°C to 70°C, including but not limited to 40°C, 50°C, 60°C, 70°C, and the time is 12h to 48h, including but not limited to 12h, 20h, 24h, 30h, 36h, 40h, 48h.

[0088] In some embodiments, the temperature for heating and curing is 60°C and the time is 24h.

[0089] It is understandable that the polymer electrolyte provided by the present invention is obtained by in-situ thermal polymerization, which can form good interfacial contact and effectively reduce the interfacial impedance. At the same time, the present invention uses an ionic liquid as a solvent. After in-situ thermal polymerization, the resulting electrolyte does not contain flammable solvents, avoiding the problems that the residual flammable solvents after thermal polymerization affect the battery safety performance or require further treatment.

[0090] In a third aspect of the present invention, a secondary battery is provided, which includes a positive electrode plate, a negative electrode plate, a separator, and a non-flammable polymer electrolyte.

[0091] The non-flammable polymer electrolyte is the non-flammable polymer electrolyte described in the first aspect above, or the non-flammable polymer electrolyte prepared by the preparation method described in the second aspect above.

[0092] It is understandable that the present invention does not limit the positive electrode plate, negative electrode plate, and separator of the secondary battery, and any limitation that can achieve the purpose of the present invention is within the protection scope of the present invention. Exemplarily, the negative electrode of the present invention can be prepared by cutting a lithium-copper composite tape with a certain lithium layer thickness into a standby state. Preferably, the lithium layer thickness is 20 μm; the cutting size is 60 mm × 100 mm. The positive electrode of the present invention can be prepared by the following method: after mixing the positive electrode active material, conductive agent, and binder, adding a solvent and mixing evenly to obtain a slurry; uniformly coating the slurry on the positive electrode current collector and drying it. Among them, the positive electrode active material can be exemplarily selected as LiNi 0.8 Co 0.1 Mn 0.1 O2; the conductive agent is conductive carbon black (Super P); the binder is polyvinylidene fluoride (PVDF), the solvent is N-methylpyrrolidone (NMP); the weight ratio of the positive electrode active material, conductive agent, and binder can be selected as 8:1:1. The drying temperature is 90 °C. The positive electrode can be cut into the required specifications during use, such as 60 mm × 100 mm. The positive electrode current collector can be selected as aluminum foil. The separator can be selected as a polyethylene (PE) separator.

[0093] In some embodiments, the secondary battery is a lithium battery.

[0094] In some embodiments, the electrolyte precursor is injected into a battery cell including the positive electrode plate, the separator, and the negative electrode plate, and in-situ heated and cured to form the non-flammable polymer electrolyte.

[0095] The following are specific embodiments.

[0096] Example 1

[0097] (1) Preparation of the negative electrode plate

[0098] The lithium-copper composite tape with a lithium layer thickness of 20 μm was cut into a size of (60 mm × 100 mm) for standby.

[0099] (2) Preparation of the positive electrode plate

[0100] The positive ternary active material LiNi 0.8 Co 0.1 Mn 0.1 O2, conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 8:1:1, and an appropriate amount of N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 75%. The slurry was stirred evenly and then uniformly coated on the positive current collector aluminum foil and dried at 90 °C to obtain the positive electrode plate. The positive electrode plate was cut into a size of (60 mm × 100 mm) for standby.

[0101] (3) Preparation of the polymer electrolyte precursor solution

[0102] 30 g of Compound 1, 30 g of diethyl vinyl phosphate, 4 g of triallyl phosphate, and 15 g of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide were weighed and mixed evenly. Then, 1 g of azobisisobutyronitrile and 20 g of lithium bis(trifluoromethylsulfonyl)imide were added and stirred until completely dissolved to obtain the polymer electrolyte precursor solution.

[0103] (4) Preparation of the lithium battery

[0104] A polyethylene (PE) separator with a thickness of 12 μm was selected and stacked in a Z-shaped manner. The positive electrode plate and the negative electrode plate prepared above were respectively on both sides of the separator, and the separator was between the electrode plates. After stacking, the electrode tabs were welded, and then placed into an aluminum-plastic film. The top and side sealing, injection of the polymer precursor solution prepared in step (3), encapsulation, normal temperature infiltration, and heat curing (60 °C, 24 h) were carried out, and finally a soft-pack battery was obtained.

[0105] Example 2

[0106] It is basically the same as Example 1, except that for the preparation of the polymer electrolyte precursor solution in step (3), it is as follows:

[0107] 40 g of Compound 1, 20 g of diethyl vinyl phosphate, 4 g of triallyl phosphate, and 15 g of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide were weighed and mixed evenly. Then, 1 g of azobisisobutyronitrile and 20 g of lithium bis(trifluoromethylsulfonyl)imide were added and stirred until completely dissolved to obtain the polymer electrolyte precursor solution.

[0108] Example 3

[0109] Basically the same as Example 1, except that for the preparation of the polymer electrolyte precursor solution in step (3), it is as follows:

[0110] Weigh 20 g of Compound 1, 40 g of diethyl vinyl phosphate, 4 g of triallyl phosphate, and 15 g of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide and mix them evenly. Then continue to add 1 g of azobisisobutyronitrile and 20 g of lithium bis(trifluoromethanesulfonyl)imide, and stir until completely dissolved to obtain a polymer electrolyte precursor solution.

[0111] Example 4

[0112] Basically the same as Example 1, except that for the preparation of the polymer electrolyte precursor solution in step (3), it is as follows:

[0113] Weigh 30 g of Compound 1, 30 g of diethyl vinyl phosphate, 2 g of triallyl phosphate, and 17 g of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide and mix them evenly. Then continue to add 1 g of azobisisobutyronitrile and 20 g of lithium bis(trifluoromethanesulfonyl)imide, and stir until completely dissolved to obtain a polymer electrolyte precursor solution.

[0114] Example 5

[0115] Basically the same as Example 1, except that for the preparation of the polymer electrolyte precursor solution in step (3), it is as follows:

[0116] Weigh 30 g of Compound 1, 30 g of diethyl vinyl phosphate, 8 g of triallyl phosphate, and 11 g of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide and mix them evenly. Then continue to add 1 g of azobisisobutyronitrile and 20 g of lithium bis(trifluoromethanesulfonyl)imide, and stir until completely dissolved to obtain a polymer electrolyte precursor solution.

[0117] Example 6

[0118] Basically the same as Example 1, except that for the preparation of the polymer electrolyte precursor solution in step (3), it is as follows:

[0119] Weigh 30 g of Compound 2, 30 g of diisopropyl vinyl phosphate, 4 g of triallyl phosphate, and 15 g of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide and mix them evenly. Then continue to add 1 g of azobisisobutyronitrile and 20 g of lithium bis(trifluoromethanesulfonyl)imide, and stir until completely dissolved to obtain a polymer electrolyte precursor solution.

[0120] Example 7

[0121] Basically the same as Example 1, except that for the preparation of the polymer electrolyte precursor solution in step (3), it is as follows:

[0122] Weigh 30 g of Compound 1, 30 g of diethyl vinylphosphonate, 4 g of triallyl phosphite, and 15 g of N-methyl-N-butylpyrrolidinium bis(trifluoromethanesulfonyl)imide and mix them evenly. Then, add 1 g of azobisisobutyronitrile and 20 g of lithium bis(trifluoromethanesulfonyl)imide, and stir until completely dissolved to obtain a polymer electrolyte precursor solution.

[0123] Example 8

[0124] It is basically the same as Example 1, except that for the preparation of the polymer electrolyte precursor solution in step (3), it is as follows:

[0125] Weigh 30 g of Compound 1, 30 g of diethyl vinylphosphonate, 4 g of triallyl phosphate, and 15 g of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide and mix them evenly. Then, add 1 g of azobisisobutyronitrile and (10 g of lithium bis(trifluoromethanesulfonyl)imide + 10 g of lithium bis(fluorosulfonyl)imide), and stir until completely dissolved to obtain a polymer electrolyte precursor solution.

[0126] Comparative Example 1

[0127] It is basically the same as Example 1, except that for the preparation of the polymer electrolyte precursor solution in step (3), it is as follows:

[0128] Weigh 22 g of Compound 1, 30 g of diethyl vinylphosphonate, 4 g of triallyl phosphate, and 23 g of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide and mix them evenly. Then, add 1 g of azobisisobutyronitrile and 20 g of lithium bis(trifluoromethanesulfonyl)imide, and stir until completely dissolved to obtain a polymer electrolyte precursor solution.

[0129] Comparative Example 2

[0130] It is basically the same as Example 1, except that for the preparation of the polymer electrolyte precursor solution in step (3), it is as follows:

[0131] Weigh 34 g of Compound 1, 30 g of diethyl vinylphosphonate, 4 g of triallyl phosphate, and 11 g of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide and mix them evenly. Then, add 1 g of azobisisobutyronitrile and 20 g of lithium bis(trifluoromethanesulfonyl)imide, and stir until completely dissolved to obtain a polymer electrolyte precursor solution.

[0132] Comparative Example 3

[0133] It is basically the same as Example 1, except that for the preparation of the polymer electrolyte precursor solution in step (3), it is as follows:

[0134] Weigh 30 g of methyl methacrylate, 30 g of diethyl vinylphosphonate, 4 g of triallyl phosphate, and 15 g of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide and mix them evenly. Then continue to add 1 g of azobisisobutyronitrile and 20 g of lithium bis(trifluoromethanesulfonyl)imide, and stir until completely dissolved to obtain a polymer electrolyte precursor solution.

[0135] Comparative Example 4

[0136] It is basically the same as Example 1, except that for the preparation of the polymer electrolyte precursor solution in step (3), it is specifically as follows:

[0137] Weigh 60 g of Compound 1, 4 g of triallyl phosphate, and 15 g of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide and mix them evenly. Then continue to add 1 g of azobisisobutyronitrile and 20 g of lithium bis(trifluoromethanesulfonyl)imide, and stir until completely dissolved to obtain a polymer electrolyte precursor solution.

[0138] Comparative Example 5

[0139] It is basically the same as Example 1, except that for the preparation of the polymer electrolyte precursor solution in step (3), it is specifically as follows:

[0140] Weigh 30 g of Compound 1, 30 g of diethyl vinylphosphonate, 4 g of triallyl phosphate, and 15 g of ethylene carbonate and mix them evenly. Then continue to add 1 g of azobisisobutyronitrile and 20 g of lithium bis(trifluoromethanesulfonyl)imide, and stir until completely dissolved to obtain a polymer electrolyte precursor solution.

[0141] Comparative Example 6

[0142] It is basically the same as Example 1, except that for the preparation of the polymer electrolyte precursor solution in step (3), it is specifically as follows:

[0143] Weigh 20 g of Compound 1, 45 g of diethyl vinylphosphonate, 4 g of triallyl phosphate, and 10 g of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide and mix them evenly. Then continue to add 1 g of azobisisobutyronitrile and 20 g of lithium bis(trifluoromethanesulfonyl)imide, and stir until completely dissolved to obtain a polymer electrolyte precursor solution.

[0144] Comparative Example 7

[0145] It is basically the same as Example 1, except that for the preparation of the polymer electrolyte precursor solution in step (3), it is specifically as follows:

[0146] Weigh 40 g of Compound 1, 15 g of diethyl vinylphosphonate, 4 g of triallyl phosphate, and 20 g of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide and mix them evenly. Then, add 1 g of azobisisobutyronitrile and 20 g of lithium bis(trifluoromethanesulfonyl)imide, and stir until completely dissolved to obtain a polymer electrolyte precursor solution.

[0147] Comparative Example 8

[0148] It is basically the same as Example 1, except that for the preparation of the polymer electrolyte precursor solution in step (3), it is specifically as follows:

[0149] Weigh 30 g of Compound 1, 30 g of diethyl vinylphosphonate, 4 g of triallyl phosphate, and 15 g of N-methyl-N-butylpiperidinium bis(trifluoromethanesulfonyl)imide and mix them evenly. Then, add 1 g of azobisisobutyronitrile and 20 g of lithium bis(trifluoromethanesulfonyl)imide, and stir until completely dissolved to obtain a polymer electrolyte precursor solution.

[0150] Comparative Example 9

[0151] (1) Preparation of the negative electrode sheet

[0152] Cut a lithium-copper composite tape with a lithium layer thickness of 20 μm into a size of (60 mm × 100 mm) for later use.

[0153] (2) Preparation of the positive electrode sheet

[0154] Mix the positive ternary active material LiNi 0.8 Co 0.1 Mn 0.1 O2, conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) in a weight ratio of 8:1:1, add an appropriate amount of N-methylpyrrolidone (NMP) as a solvent, and prepare a slurry with a solid content of 75% and stir evenly. Coat the slurry evenly on the positive current collector aluminum foil, dry it at 90 °C to obtain a positive electrode sheet, and cut the positive electrode sheet into a size of (60 mm × 100 mm) for later use.

[0155] (3) Preparation of the lithium battery

[0156] Select a polyethylene (PE) separator with a thickness of 12 μm, and use the Z-shaped lamination method. The positive electrode sheet and the negative electrode sheet are respectively on both sides of the separator, and the separator is between the electrode sheets. After lamination, weld the tabs, then place them in an aluminum-plastic film, perform top-side sealing, inject a conventional electrolyte (1 M LiPF6 in EC:DEC = 3:7 V / V, 5 wt% FEC), encapsulate, soak at room temperature, and heat and cure (60 °C, 24 h) to finally obtain a soft-pack battery.

[0157] Test Example:

[0158] (1) Ion conductivity test

[0159] Cut a 12-μm-thick PE separator into 19-mm-diameter circular pieces, place them between two stainless-steel sheets (16 mm in diameter), and drop the polymer electrolyte precursor solutions prepared in the examples and comparative examples onto the separators respectively. After soaking at room temperature for 12 h, cure them at 55 °C for 24 h. Use an electrochemical workstation to measure the resistance at different temperatures through AC impedance, and then calculate the ion conductivity of the membrane at different temperatures through formula (1). The results are shown in Table 1. Formula (1) is as follows:

[0160] σ = t / (R×S) (1)

[0161] Where: σ is the ion conductivity (S / cm), t is the thickness of the ion-exchange membrane (cm), R is the in-plane resistance perpendicular to the membrane surface (Ω), and S is the effective membrane area (cm 2 ²).

[0162] (2) Ignition test

[0163] To evaluate the flame retardancy of the polymer electrolyte, first pour the polymer electrolyte precursor solutions of the examples and comparative examples into polytetrafluoroethylene molds (10 mm×10 mm) respectively, and heat and cure them (60 °C, 24 h) to obtain polymer electrolyte samples. Then, conduct an ignition test on the polymer electrolyte samples with a butane flame, observe their combustion behavior, and calculate the self-extinguishing time (SET) using the following formula (2). The results are shown in Table 1. Formula (2) is as follows:

[0164] SET = t b / m e (2)

[0165] Where SET is the self-extinguishing time, in units of sec / g; t b is the total combustion time of the electrolyte, in units of seconds (sec); m e is the total mass of the electrolyte, in units of g.

[0166] Table 1: Performance parameters of the polymer electrolytes in the examples and comparative examples

[0167] Serial number Ionic conductivity (mS / cm) SET (sec / g) Example 1 1.83 4.1 Example 2 2.75 9.2 Example 3 1.36 1.1 Example 4 2.24 7.3 Example 5 1.21 2.2 Example 6 1.67 4.5 Example 7 1.79 4.8 Example 8 2.15 3.9 Comparative Example 1 0.91 9.3 Comparative Example 2 1.10 15.8 Comparative Example 3 0.36 0.5 Comparative Example 4 3.02 42.4 Comparative Example 5 1.53 19.2 Comparative Example 6 0.86 3.6 Comparative Example 7 2.32 24.3 Comparative Example 8 1.01 5.2 Comparative Example 9 4.12 69.3

[0168] As can be seen from Table 1, the polymer electrolyte provided by the present invention has both high ion conductivity and flame retardancy.

[0169] (3) Cycle performance test

[0170] The cycle tests of the lithium batteries prepared in the examples and comparative examples were carried out on a Neware test system. The batteries were charged / discharged in a constant current-constant potential charging / constant current discharging (CC-CV / DC) mode. The cut-off voltages for charging and discharging were 4.2 V and 2.8 V respectively, and the cut-off current for the constant potential was 0.05 C. The batteries were left to stand for 5 minutes between each charge and discharge cycle. The batteries were cycled at a charge / discharge rate of 0.2 / 0.5 C at 25 °C. The test results are shown in Table 2.

[0171] (4) Battery safety performance test

[0172] After charging the lithium batteries obtained in the above examples and comparative examples to 4.2 V respectively, they were heated at a heating rate of 10 °C / min until the battery core smoked or caught fire and failed. The temperature at the time of failure was recorded as the thermal failure temperature of the battery core, and the combustion or smoking situation at the time of failure was observed. The test results are shown in Table 2.

[0173] Table 2: Test data of the batteries in the examples and comparative examples

[0174]

[0175]

[0176] As can be seen from Table 2, the batteries using the polymer electrolyte provided by the present invention not only have high safety performance but also can maintain excellent cycle performance.

[0177] Combined with Table 1 and Table 2, the performance of the polymer electrolyte and the battery containing the polymer electrolyte is analyzed: Comparative Example 1 and Comparative Examples 1-2 show that when the ratio of lithium-conducting monomer to solvent is less than 1.2:1 or greater than 2.9:1, the ionic conductivity of the polymer electrolyte will decrease, showing poor cycle performance. Comparative Example 1 and Comparative Example 3 show that since Comparative Example 3 only uses flame-retardant monomers and does not add lithium-conducting monomers, the polymer electrolyte obtained has outstanding flame retardancy, but low ionic conductivity, showing poor cycle life. Comparative Example 1 and Comparative Example 4 show that since Comparative Example 4 only uses lithium-conducting monomers and does not add flame-retardant monomers, the polymer electrolyte formed has high ionic conductivity, but poor flame retardancy, resulting in poor battery safety performance. Comparative Example 1 and Comparative Example 5 show that when ordinary solvents are used instead of ionic liquids, the ionic conductivity and flame retardancy of the polymer electrolyte will decrease. This is because the solvent of the comparative example itself is flammable and cannot effectively regulate the interaction between the lithium-conducting monomer and lithium ions, thereby reducing the ionic conductivity. Comparative Example 1 and Comparative Examples 6 to 7 show that when the mass of the lithium-conducting monomer and the solvent and the proportion of the total mass of the lithium-conducting monomer, the solvent and the flame-retardant monomer are less than 42%, the ionic conductivity of the polymer electrolyte decreases, and the corresponding battery cycle performance also decreases significantly. When the proportion is higher than 75%, the flame retardancy of the polymer electrolyte decreases, and the safety of the corresponding battery also deteriorates significantly. Comparative Example 1 and Comparative Example 8 show that when the viscosity and conductivity of the selected ionic liquid solvent are not appropriate, it will affect its regulatory effect on the lithium-conducting monomer and lithium ions, thereby affecting the cycle stability of the prepared battery. Comparative Example 1 and Comparative Example 9 show that since Comparative Example 9 uses a conventional liquid electrolyte, the proportion of flammable carbonate solvent is high, and the battery safety performance is extremely poor.

[0178] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0179] The above is only a preferred embodiment of the present invention, and the present invention is not limited to the above embodiments. It is understood that other improvements and changes directly derived or associated by those skilled in the art without departing from the spirit and concept of the present invention should be considered to be included in the protection scope of the present invention.

Claims

1. A non-combustible polymer electrolyte, characterized in that, The preparation raw materials of the non-combustible polymer electrolyte at least include a lithium-conducting monomer, a flame retardant monomer, and a solvent; The lithium-conducting monomer includes a monomer having an acryloyl group and a morpholine group; the flame retardant monomer includes a vinyl phosphorus-containing monomer; the solvent includes an ionic liquid; wherein, 2. The non-combustible polymer electrolyte according to claim 1, wherein The mass ratio of the lithium-conducting monomer to the solvent is 1.2-2.9:

1.

3. The non-combustible polymer electrolyte according to claim 1, characterized in that, The lithium-conducting monomer includes at least one of the following structural formulas: Preferably, in the preparation raw materials of the non-combustible polymer electrolyte, the mass fraction of the lithium-conducting monomer is 20%-40%.

4. The non-combustible polymer electrolyte according to claim 1, characterized in that, The flame retardant monomer includes at least one of dimethyl vinyl phosphate, diethyl vinyl phosphate, dipropyl vinyl phosphate, and diisopropyl vinyl phosphate; Preferably, in the preparation raw materials of the non-combustible polymer electrolyte, the mass fraction of the flame retardant monomer is 20%-40%.

5. The non-flammable polymer electrolyte according to claim 1, characterized in that, In the preparation raw materials of the non-combustible polymer electrolyte, the mass fraction of the solvent is 10%-18%; Preferably, the ionic liquid includes a fluorosulfonamide-based anion; Preferably, the ionic liquid satisfies at least one of items (1)-(2): (1) At 25°C and 1 atm, the conductivity ≥ 0.1 S / m; (2) At 25°C and 1 atm, the viscosity ≤ 0.1 Pa·s; Preferably, the ionic liquid includes at least one of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-butyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide, and N-methyl-N-butylpyrrolidinium bis(trifluoromethylsulfonyl)imide.

6. The non-combustible polymer electrolyte according to any one of claims 1 to 5, characterized in that, The preparation raw materials of the non-combustible polymer electrolyte further include a cross-linking monomer, a lithium salt, and an initiator.

7. The non-combustible polymer electrolyte according to claim 6, characterized in that, The cross-linking monomer includes a monomer containing more than 2 vinyl groups; Preferably, the cross-linking monomer includes at least one of triallyl phosphate and triallyl phosphite; Preferably, in the preparation raw materials of the non-combustible polymer electrolyte, the mass fraction of the cross-linking monomer is 2%-8%.

8. The non-combustible polymer electrolyte according to claim 6, characterized in that, The lithium salt includes a fluorosulfonamide-type lithium salt; Preferably, the lithium salt includes at least one of lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium hexafluorophosphate; Preferably, in the preparation raw materials of the non-combustible polymer electrolyte, the mass fraction of the lithium salt is 10%-30%; The initiator includes at least one of benzoyl peroxide, potassium persulfate, ammonium persulfate, azobisisobutyronitrile, and azobisisoheptonitrile; Preferably, in the preparation raw materials of the non-combustible polymer electrolyte, the mass fraction of the initiator is 0.5%-1.5%.

9. A method for preparing the non-combustible polymer electrolyte according to any one of claims 6 to 8, characterized in that, The preparation method includes the following steps: Mix the lithium-conducting monomer, the flame retardant monomer, the cross-linking monomer, and the solvent evenly, add the initiator and the lithium salt, and mix to obtain an electrolyte precursor; Heat and cure to obtain a non-combustible polymer electrolyte; Preferably, the temperature of the heat curing is 40°C-70°C, and the time is 12h-48h; More preferably, the temperature of the heat curing is 60°C, and the time is 24h.

10. A secondary battery, characterized in that, It includes a positive electrode plate, a negative electrode plate, a separator, and a non-combustible polymer electrolyte; The non-flammable polymer electrolyte is the non-flammable polymer electrolyte described in any one of claims 1 to 8, or the non-flammable polymer electrolyte prepared by the preparation method described in claim 9; Preferably, the secondary battery is a lithium battery; More preferably, the electrolyte precursor is injected into the positive electrode sheet, the separator, and the negative electrode sheet stacked in sequence, and in-situ heated and cured to form the non-flammable polymer electrolyte.

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